Current non-military Global Positioning Systems (GPS) use L1/L2 dual frequency antennas. Dual frequency antennas are more difficult to design and manufacture than are single frequency antennas. Hence, dual frequency antennas command a premium price. Thus, it is reasonable to assume that antennas that can receive signals at three or more frequencies are all the more complex and expensive to design.
With the advent of modernization of GPS, GPS satellites are on track to offer more frequencies, such as unencrypted L2 and L5 signals. Further, future Global Navigation Satellite System (GNSS) constellations are expected to offer more frequencies than are available from present day GPS constellations. For example, Galileo will offer signals at 1278.75 MHz and 1207.14 MHz. Thus, it is likely that antennas with a passband at three or more frequencies will be needed in the near future. In this context, a passband refers to a frequency band selection property of the antenna, wherein, radio signals in the range of frequencies of the passband are passed (admitted), but radio signals outside of the range of frequencies of the passband are attenuated (rejected). In general, the passband characteristics of an antenna are determined by one or more of: the antenna element and ground-plane design, the optional amplifier and the optional filtering electronics. In addition to being expensive, multi-passband antennas are expected to perform less well than antennas that operate at only one or two passbands.
Likely performance degradation of multi-passband antennas involve design attributes such as:                Multipath mitigation at all frequencies        Antenna gain as a function of frequency and antenna relative azimuth and/or elevation        Phase center collocation at different frequency bands        Phase center stability        
Based on the foregoing, there is a need for a system that achieves the benefits of an antenna that operates at a multiplicity of passbands without the expense, design complexity and performance degradation that are usually associated with multi-passband antennas.